Dry lubricant containing fibers and method of using the same

ABSTRACT

A dry lubricant comprises at least 50 wt % of fibers having a diameter between 50 nm and 10 microns and a length that is at least 5 times the diameter.

CROSS-REFERENCE

The present application claims priority to U.S. provisional applicationNo. 61/406,416 filed on Oct. 25, 2010, U.S. provisional application No.61/418,081 filed on Nov. 30, 2010, U.S. provisional application No.61/421,985 filed on Dec. 10, 2010 and U.S. provisional application No.61/426,083 filed on Dec. 22, 2010, the contents of all of which areincorporated by reference as if fully set forth herein.

TECHNICAL FIELD

The present invention relates to a dry lubricant comprising fibers and amethod of using the same.

RELATED ART

U.S. Pat. No. 6,482,780 discloses a grease composition for a rollerbearing comprising a metal soap-based thickening agent containing a longfiber-like material having a major axis length of at least 3 micronsincorporated in a base oil comprising a lubricant having a polar groupin its molecular structure and a non-polar lubricant blended incombination.

U.S. Pat. No. 5,415,791 discloses a lubricating composition for solidlubricant-embedded sliding members comprising 5 to 78% by weight of asolid lubricant powder material, 5 to 30% by weight of a lubricating oilwhich is in a liquid or paste form at ordinary temperatures, 1 to 15% byweight of a carrier for absorbing and retaining said lubricating oil,and 15 to 50% by weight of a thermosetting synthetic resin binder. Thecarrier may be an oleophilic fiber, such as cellulose fiber andpolypropylene fiber.

U.S. Pat. No. 7,150,775 discloses a powder metal composition comprisinga ferrous metal powder and a modified lubricant consisting essentiallyof a lubricant powder and comminuted cellulose fibers having an averagelength less than 70 μm and a diameter in the range from about 1-20 um.The modified lubricant is present in an amount less than 2% by weight ofthe composition.

SUMMARY

It is an object of the present teachings to disclose an improved drylubricant and a method for lubricating a surface using the drylubricant.

This object is achieved by the invention of claims 1 and 27,respectively.

Further developments of the invention are recited in the dependentclaims.

According to a first aspect of the present teachings, a dry lubricantcomprises at least 50 wt % of fibers having a diameter between 50 nm and10 microns and a length that is at least 5 times the diameter. Morepreferably, the fibers have a diameter between 100 nm and 1 micron. Thefibers are preferably comprised of a polymeric material that has beenspun into fibers.

In another aspect of the present teachings, the dry lubricant preferablycomprises at least two types of said fibers, each having a differentmelting temperature. Preferably, at least the fiber having the lowestmelting temperature acts as a lubricant when the dry lubricant isbrought to a temperature above the melting temperature of said fiber.

According to this aspect of the present teachings, at least one of thetwo types of fibers is preferably comprised of a wax material, such as anatural wax or a hydrocarbon wax, more preferably bees wax or paraffinwax.

In addition or in the alternative, at least one of the two types offibers is comprised of PTFE and/or PES.

In another aspect of the present teachings, the fibers may be loosestrands. The fiber strands optionally may be adhered or cross-linked bya compound having a lower molecular weight than the fibers, such as alow molecular weight wax compound.

In addition or in the alternative, the fibers according to the presentteachings may be disposed on a surface in need of lubrication. Thefibers may act as a lubricant in the solid state, or at least some ofthe fibers may melt at a temperature below the normal operatingtemperature of the surface in need of lubrication. In the latter case,at least the melted fiber material acts as a lubricant.

Since the fibers can be produced from a wide range of materials, thepresent teachings advantageously enable a wide flexibility or choice inthe selection of the structuring (fiber or fibrous) material. Thematerial can be selected to satisfy very specific operating conditionsand/or to impart the dry lubricant with advantageous properties, such astemperature stability, lubricating performance, etc. Thus, according tothis aspect of the present teachings, refinements are possible in thephysics and chemical tuning of the performance (lubrication, fiberreinforcing, etc) as well as the particular processes for making anddelivering this dry lubricant into the systems in need of lubrication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows oil reservoirs defined in an elastomeric seal lip accordingto one aspect of the present teachings.

FIG. 2 shows a seal according to the present teachings having a porousliner layer disposed on the seal lip portion.

FIG. 3 is a graph showing the changes in grease consistency relative tofiber density according to experimental examples of the presentteachings.

DETAILED DESCRIPTION OF THE INVENTION

In some aspects of the present teachings, the dry lubricants also may beutilized with a wide variety of fluids, e.g., oils or other baselubricating fluids, that exhibit lubricating properties at the operatingtemperatures appropriate for various applications.

Particularly suitable lubricants (oils) include, but are not limited to,mineral oils obtained from crude oil, group I, II and III lubricants,group IV lubricants (polyalphaolefins “PAO”) and group V lubricants (allothers).

A more particular, but non-limiting, list of lubricating oils includesmineral oils, synthetic esters, and plant-based oils and theirderivatives, such as oils derived from rapeseed, canola, sunflower,canola, and palm. Animal-based oils, their derivatives and syntheticlubricants also may be suitably used in certain aspects of the presentteaching including, but not limited to, polyglycols (PG), polyalkyleneglycol (PAG), white oils, silicone oils, very-high viscosity index oils(VHVI), water, glycerol and waxes.

Particularly preferred oils according to the present teachings aremineral oils, synthetic esters, PAOs and synthetic hydrocarbons.

The viscosity of the lubricating fluid (oil) can range from very low(below 1 cSt at 40° C.) to very high (several 1000 cSt at 40° C.). Themost suitable viscosity depends on the application temperature,operating (e.g., rotating) speed, etc., and the present teachingsprovide for a wide variety of possible lubricating properties. However,particularly preferred are any of the above oil types that have aviscosity between 10 and 300 cSt at 40° C.

The fibers according to the present teachings can be made, e.g., fromany type of polymeric materials that can be spun into fibers, as well asin conjunction with optional additives. Suitable polymers include, butare not limited to, polyamide (PA), nylon 6,6, polyamide-6,6 (PA-6,6),polyamide-4,6 (PA-4,6), polyurethanes (PU), polybenzimidazole (PBI),polycarbonate (PC), polyacrylinitrile (PAN), acrylonitrile rubber (NBR),polyvinylalcohol (PVA), polylactic acid (PLA),polyethylene-co-vinyl-acetate (PEVA), polymethacryate (PMMA),tetrahydroperfluorooctylacrylate (TAN), polyethylene oxide (PEO),collagen-PEO, polyaniline (PANI), polystyrene (PS), silk-like polymerwith fibronectin functionality, polyvinylcarbazole, polyethyleneterephtalate (PET), polyacrylic acid (PAA), polypyrene methanol (PM),polyvinylphenol (PVP), polyvinylchloride (PVC), cellulose acetate (CA),polyacrylamide (PAA), poly(lactic-co-glycolic acid) (PLGA), collagen,polycaprolactone (PCL), poly(2-hydroxyethyl methacrylate) (HEMA),poly(vinylidene fluoride) (PVDF), polyether imide (PEI), polyethyleneglycol (PEG), poly(ferrocenyldimethylsilane) (PFDMS),poly(ethylene-co-vinyl alcohol), polyvinyl pyrrolidone (PVP),polymetha-phenylene isophthalamide, polypropylene (PP), polyethylenenaphthalate (PEN), Teflon®, polytetrafluorethene (PTFE), waxes, waxypolymers, polyolefins, polyesters, polysulfones and polyether sulfones(PES).

PP, PA, PTFE and PES are preferred.

In addition or in the alternative, polymers derived from natural orbiodegradable sources are also suitable for making fibers that can beutilized with the present teachings, in particular for the production ofbiodegradable greases. Representative examples of such polymers include,but are not limited to, polysaccharides, such as cellulose, starch,chitin, chitosan, proteins, (poly)peptides and gelatin.

Of course, mixtures or blends of two or more of the above-noted polymersare suitable as well. All possible combinations of two or more of theabove-mentioned polymers are understood as being expressly enumeratedfor the purposes of original description.

In one aspect of the present teachings, a small fraction (e.g., 0.1-5%)of fibers of one type can be added to grease that primarily contains asecond type of fiber so as to impart special properties to the grease.For example, the fibers can be designed to melt at elevated temperaturesto form a lubricant. In addition or in the alternative, the fibers cancontain additives. In addition or in the alternative, the fibers canprovide a structural function in the lubricant or grease.

Mixtures of two types of fibers A and B in a ratio A:B between 10:90 and50:50 can be utilized to impart unique properties to the lubricant orgrease.

The fibers can be between 0.1 and 100 wt % of the final material. Amaterial having 50-100 wt % of fiber can also function as a ‘dry’lubricant, preferably if part or all of the fiber melts underapplication (usage) conditions (e.g., pressure, temperature, shearstress) and forms a lubricant.

At increasing fiber density, the consistency will increase, which is asignificant grease composition parameter. The most suitable fiberdensities will depend on the desired grease consistency for a particularapplication (usage).

In another aspect of the present teachings, a micro/nano fiber networkcan be prepared that will naturally embed, incorporate or absorb oil oranother suitable base lubricating fluid, such that the overall processfor making the lubricant is simplified to a great extent. Fibers can bemade from a variety of different materials mentioned above and thelength/diameter ratio of the fibers, as well as the chemical composition(bulk or surface) thereof, can be tuned or suitably selected, as wasmentioned above, using a variety of different existing processes thatare inherently low cost in nature. The construction of a soap-like orsponge-like structure by forming a cloth, pad, fabric, mat orsponge-like network from the fibers described herein, or byappropriately dispersing the fibers in an appropriate lubricant, leadsto the generation of new lubricants with one or more specific propertiesthat are believed to be new in the grease/lubricant field.

Thus, in another aspect of the present teachings, a cloth, pad, fabricor mat material can be produced from a variety of different polymermaterials, such as the fiber materials mentioned above. In addition, thecloth material may also be made with suitable lubrication additivesincluded within or in the surface of the fibrous network, e.g., anon-woven fibrous network. This provides flexibility in producingunique, low weight structures that will only require the addition of anoil or another base lubricating fluid in order to form the lubricant,such as a grease. The properties of the fibers can be tuned or suitablyselected or treated in order to adjust the physical properties (e.g.,length, diameter, mixture, etc.) and/or the chemical properties (surfacetreatment, bulk material, wetting behavior, etc.), which selectionand/or treatment will enable the fibers to be suitably adapted to anytype of lubricating fluid.

In other embodiments, the fibers can be cut to a specific length andthus the fibers can be utilized in a loose or dispersable state. Inanother method for preparing fibers of a shorter length then has beenavailable in the past, a cloth or fabric made of the fibers may befrozen and then the polymeric fibers are crushed while they are in abrittle state.

Such non-woven fiber fabrics mats can be made, e.g., by melt blowingmicron or sub-micron diameter fibers, or by electro-spinning Inaddition, fiber material mats/cloths that may be advantageously utilizedwith the present teachings can also be obtained from commercial sources,such as Hills Inc. of W. Melbourne, Flo., U.S.A.

A soap-like structure made of micro/nano fibers will not require aheating and cooling process to form the grease, or will require only aminimal heating/cooling process. The fiber network may be organic and/orinorganic. The fiber fabrication method may be made compatible with avery large volume production.

The diameter of the fibers is preferably in the micron or nanometerrange, while the length of the fibers is preferably in the range ofseveral to tens of microns, most preferably less than 30 microns (μm).Preferably, nanoparticle materials (i.e. nanometer-sized particleshaving a low aspect ratio, e.g., about 1) that could present healthhazards, which would limit their application, may be avoided.

The fiber diameters are between 50 nm and 10 microns, more preferablybetween 100 nm and 1 micron. Further, the fibers have a length that isat least 5-10 times the diameter thereof. That is, the fibers preferablyhave an aspect ratio of at least 5 to 10. The length of the fibers canbe suitably modified to effect desirable changes to the structuralproperties of the dry lubricant, its mechanical stability, and its bulkrheological properties. Thus, the fiber length can be optimized forparticular application (usage) conditions.

The base material for the fibers can be produced and tuned/adapted for aspecific application. If the dry lubricant is intended to also beutilized with a lubricating fluid, the base material could be sent to afinal user as a cloth/fabric material or a network of pre-cut fibers. Inthis case, the final user would only need to add oil (and perform asimple mixing procedure) to produce the lubricant or grease. This aspectof the present teachings provides a great degree of flexibility, becausethe base material can be shipped worldwide relatively inexpensively, dueto its low weight (i.e. unlike oil or greases, which are relativelyheavy).

The dry lubricant according to the present teachings may include one ormore known additives that are commonly used in the dry lubricant field.The additives may be included to give the lubricant specialfunctionality with respect to the aging of the lubricant (e.g.,anti-oxidants), friction reducers, anti-wear, extreme pressureproperties, etc.

Additives can also be added to give the dry lubricant a strongerstructure by linking or connecting (e.g., bonding) the fibers usingsuitable polymers, waxes or the like. Fibers having different propertiescan be used as additives as well.

Other suitable additives include ceramic particulates (silica, aluminia,zirconia, etc) and metallic particles.

The additives can be added to the polymer bulk base before the fibersare produced, but could also be added to the dry fibers. Smallquantities of a carrier fluid (very suitable is a lubricant with orwithout additive) can also be added to the dry polymer base material.

The additive(s) can also be added to the oil, which is then mixed andhomogenized with the fibers or fibrous material (e.g., the cloth/fabricmade from the fibers).

In another aspect of the present teachings, the fibers themselves mayserve as an additive. For example, the fibers disclosed herein may beadded to known lubricants (e.g., oil, greases and emulsions) to improvethe lubrication and tribological performance thereof.

In another aspect of the present teachings, different materials ormaterial properties can be mixed or combined in the same fiber, therebyachieving a phase separation and heterogeneous fibers. Consequently, adifferentiated or dual behavior can be achieved in a single fiber. Suchmulti-property or multi-phase fibers may be referred to as a “JANUSfiber” after the Greek god who had two faces. Such multi-property ormulti-phase fibers are highly advantageous to the development ofmechanical stability (when needed) and to the ability of thelubricant/grease to self heal. That is, after some type of disruptivemechanical action (e.g. shearing), the fiber structure may preferablyheal itself (e.g., self re-assembly) once again into the desiredstructure (network).

The Janus fibers can be produced according to a variety of methods. Forexample, the fibers can be subjected to a spray treatment, a plasmatreatment and/or deposition process that exposes the fiber on one side.A deposition material can be a metal, polymer, small ceramic, metallicor organic nano-particulates that is/are embedded into or attached tothe fiber on one side, e.g., the exposed side. This can be done eitherduring the production of the fibers or after the production thereof. Thedeposition will create fibers with different properties on the exposedand the unexposed sides. Another way is to prepare two different typesof polymers in parallel and then form them into one single fiber usingexisting micro-scale extrusion techniques. These are sometimes referredto as Island-In-Sea fibers in which a plurality of nano or micron-scale(bi-component) fibers are extruded in a matrix of a third polymer.

Another aspect of the present teachings relates to improve drylubricants, e.g., for bearings, linear actuators, gears and any othermechanical raceway, track or sliding surface.

For example, in this aspect, fibers of the present teachings can berubbed onto (or otherwise applied to or deposited on) a sliding surfaceof a device, such as the raceway of a bearing, a gear or a linear device(motor), in order to form a local deposit of the fibers. The fibers canbe applied as a preservative measure in order to provide both a better“running-in” of the device and a better long term storage resistance ofthe mechanical components. This feature of the present teachingsprovides a dry local lubrication.

Even without the mechanical pre-treatment, the present teachings may beapplied to provide a layer on the surface, which layer is made by mixinga fiber (predominantly) and lubricant or carrier fluid (minorcomponent). The resulting dynamic coating will self-regenerate duringsubsequent cycles and will protect the surface. As the fibers may bepre-treated with any suitable additives (e.g., low friction, anti-wear,and/or anti-oxidation agents), they can act as long-lasting,slow-release agents in order to enhance the lubrication function and toensure longer service life of the mechanical surfaces.

As utilized in the present teachings, the term “hydrophilic” means thatthe surface of a flat piece of the material (i.e. the material that willbe used to form the hydrophilic fibers or fibrous material) will bereadily covered (wetted) by water, because that will reduce the totalsurface energy of the system. The more hydrophilic the material is, thesmaller the “contact angle” of the drop of water on a flat smoothsurface of such material will be, which makes the contact angle asuitable measure of the degree of hydrophilicity in accordance with thepresent teachings. In principle, if a small drop of water exhibits aninner contact angle that is less 90 degrees when dropped onto amaterial, such material can be considered hydrophilic.

A higher degree of hydrophilicity of the hydrophilic fibrous materialsaccording to the present teachings (i.e. a smaller contact angle) may bemore advantageous in certain embodiments.

Similarly, as utilized in the present teachings, the term “oleophilic”means that the surface of a flat piece of the material (i.e. thematerial that will be used to form the oleophilic fibers or fibrousmaterial) will be readily covered (wetted) by oil or another baselubricating fluid, because that will reduce the total surface energy ofthe system. A porous structure of an oleophilic material will absorboil, like a sponge, through capillary action. The more oleophilic thematerial is, the smaller the “contact angle” of the drop of oil on aflat smooth surface of such material will be, which makes the contactangle a suitable measure of the degree of oleophilicity in accordancewith the present teachings. In principle, if a small drop of oilexhibits an inner contact angle that is less 90 degrees when droppedonto a material, such material can be considered oleophilic. A higherdegree of oleophilicity of the oleophilic fibrous materials according tothe present teachings (i.e. a smaller contact angle) may be moreadvantageous in certain embodiments.

Various embodiments, features and advantages of the present teachingswill now be described in more detail in the following.

Solid Lubricant or Solid Oil

In the past, known “solid oil” products have been made by saturating apolymer matrix with oil. Such solid oils have an oil content of up to70%, but are much harder than is usual for lubricating greases. Due tothe relatively stiff mechanical structure, they can provide more supportthan greases, while the relatively high oil content provides betterlubrication than can be achieved by pure polymer materials.

A fiber-thickened grease according to the present teachings can beprepared such that it has a comparable stiffness to known solid oils andsimilar materials and therefore has the same functionality. However, inthis aspect of the present teachings, performance can also be improvedas compared to known solid oils, because the fibers themselves can alsoact as a lubricant, i.e. the fibers supplement the lubricatingproperties of the base oil. For example, in such embodiments, fibrousmaterial may shear off during operation, thereby increasing the gapbetween the functional surface and the “grease” that reduces friction.If lubricating fibers enter the contact, they can provide additionallubrication.

In addition, by tuning the oleophilic properties of the present fibers,e.g., by coating or treating the fibers, the oil bleeding rate of theresulting grease can be tuned, e.g., for various bearing applications.By making a solid oil using very viscous fiber-thickened grease inaccordance with the present teachings, different solid oil products canbe easily formulated for different bearing types/operating conditions.

Such solid oils preferably have a hardness values between 1% and 100% ofthe hardness of the base material of the polymer fibers.

Thickened Lubricants

In another aspect of the present teachings, lubricants are provided inthe form thickened oils and greases. More specifically, lubricatingfluids or oils are thickened with fibers according to the presentteachings. While the most appropriate consistency is often determined bythe application or usage of the thickened lubricant, the NLGI grade orconsistency (the standard set or determined by the National LubricatingGrease Institute) is preferably equal to or greater than 00. Morepreferably, lubricants according to the present teachings have aconsistency or NLGI grade between 1 and 3, e.g., 2. Such thickenedgreases are particularly suitable for usage in bearings.

The optimal fiber density of the thickened lubricant will depend on therequired viscosity and consistency of the lubricant for the particularapplication, as well as the length and diameters of the fibers utilizedto thicken the lubricating fluid or oil. However, it is noted thatpreferred fiber weight densities (based on the total lubricant weight)for a fiber-thickened lubricant are generally between about 0.1 and 20%.Preferred fiber densities for a fiber-thickened ‘grease’ are generallyabout 2-15%, more preferably between about 5-12%. But, in case thefibers are used in conjunction with other thickeners, the fiber contentmay be reduced accordingly.

Controlled Release of Oil

In certain aspect of the present teachings, the bleeding properties ofthe oleophilic fiber-thickened lubricants and greases according to thepresent teachings can be controlled in several different ways bydesigning the fibrous structure such that it responds to an externalstimulus, such as temperature, electric signals, etc.

In one exemplary example, pH can be used to control the release of oil.In this regard, it is noted that aging of oil can lead to an increase inthe Total Acid Number (TAN) of the oil and this property can be used toincrease oil supply with time. For example, structural integrity,oleophilicity and/or shrinking of the product occur with changes in pHor specific chemicals that are released over time. In an alternativesolution according to the present teachings, the structural change andhence oil release can be triggered by the consumption of an additive.

In addition, some polymers exhibit an inverse thermal expansionbehavior, i.e. they contract or shrink with temperature increases.Fibers prepared from such polymers will act as a self regulatingbleeding pump by pumping (sponge contraction) or bleeding (releasing)more oil out of the grease when the temperature increases.

Therefore, in certain aspects of the present teachings a polymer fibercan be used that shrinks or contracts at elevated temperatures, whichwill have the effect of causing a squeezing or contraction of the fibernetwork that will, in turn, release (discharge) oil from the grease whenthe temperature increases. While such materials exist, thecontraction/shrinking is usually an irreversible process. However, thisshrinkage property may be advantageous in applications that require anemergency release of oil, which will be further described below.

In addition or in the alternative, the release mechanisms can beactivated electrically by either induced heating or by havingelectro-active polymers forming a part of the soap or network structureof the grease.

In some applications of the present lubricants (e.g., helicoptergearboxes), it may become necessary during operation to rapidly releasealmost the entire amount of oil still trapped in the fibrous network ofthe grease. Generally speaking, 90% of all oil available in thelubricant system is located inside the polymer matrix or grease soapduring normal operation.

For an emergency oil release, both gradual and fast release mechanismsare possible. In the gradual release, the inverse thermal expansionbehavior of some polymers may be advantageously utilized. As wasindicated above, the shrinkage of the polymer material at elevatedtemperatures is an irreversible mechanism, but it facilitates a gradualincrease in the release of oil as the network shrinks while thetemperature of the system increases. This shrinkage action pumps oil outof the fibrous network and into the contact where additional oil may beurgently needed to prevent a mechanical breakdown.

Another gradual release mechanism involves the use of a greasecomprising at least two different types of fibers, in which (at least)one of the fibers has a different melting point than the other(s), aswas discussed above. Initial melting of the low melting point fiber willimpart a double benefit: a faster release of oil and the transferring ofthe melted fiber to the surface that will be coated and protected.

Fast release mechanisms may involve chemical and electrical triggers toselectively dissolve or melt the fibers for a fast and irreversiblerelease of the oil buffer contained in the grease, as was discussedabove.

Improved Shelf Life

Oil separation typically takes place when grease is stored for longperiods of time, e.g., in a drum. In this case, the oil becomes visibleas an oil layer on top of the grease. In general, the oil is lighter orless dense than the soap or other thickening material, so that the oilwill float on the remaining grease. This separation phenomenon governsthe “shelf life” of the grease, i.e. the amount of time that the greasemay be safely stored before using. Release of oil ‘on the shelf’ istherefore undesirable, and this presents a challenge, because the greasemust be capable of bleeding sufficient oil in order to function as agood lubricant during operation. Therefore, shelf life and sufficientbleeding characteristics during usage need to be suitably balanced.

Oleophilic fiber-thickened greases according to the present teachingscan be prepared that exhibit a longer shelf life. In particular, twoparameters may be controlled to influence the shelf life.

First, progressive structural changes affect the thickener (fiber)structure. These are influenced by the ability of the structure toretain the oil and hence to the affinity between the oil and thestructure. A highly oleophilic structure will retain the oil better thanan oleophobic structure. Furthermore, the stability of the structure canbe optimized as described elsewhere in this specification.

Second, the buoyancy of the thickening material in the oil also affectsthe shelf life. The thickener can be designed such that the specificmass (density) is almost equal to the specific mass (density) of the oilor lubricating fluid comprised in the grease. In this case, the oil orlubricating fluid is less able to float on top of the remaining grease,because they have equal or substantially equal specific masses.

In addition or in the alternative, the fibers can be coated or treatedor thus selected in a manner that will maintain the base oil inside thefiber network (oleophilic properties) for a longer period of time.

The oleophilicity of the fibers can be determined according to a varietyof techniques that are known in the surface science field. For example,as was described above, the contact angle of a drop of oil orlubricating fluid on a smooth flat surface of the same material as thefiber may provide one indication of the oleophilicity of the fiber. Inthis case, the lower or shallower the internal contact angle, the moreoleophilic the material is. The oil is said to ‘wet’ the material whenthe internal contact angle is very shallow. Another method forindicating oleophilicity is to determine the volume of oil that a clothor other structure (e.g., fabric) made of the fibers can absorb.

The Fiber Network

As was noted above, the structure functionality and formation of thelubricant or grease can be made independent of the material.

The polymer fiber network according to the present teachings can bedesigned so that it retains solid additive particulates within the fibernetwork and independently of any treatment performed on the fibersthemselves. The size of these particulates can be nano-, micro- ormeso-scale. Particulates having a size on the order of tens of micronsare known as mesoparticles. In this aspect of the present teachings, theretention of a particulate “additives reservoir” in the fiber networkcan be provided.

Nano-, micro- and meso-scale particles having anti-wear properties (forexample, by admixing non-dissolved zinc dialkyldithiophosphate, ZDDP),anti-friction or friction-reducing properties (for example, by admixingone or more of MoS₂, WS₂, and/or PTFE), anti-oxidant properties, and/oranti-corrosion properties can be added as ingredients in the “structureforming” (i.e. fiber network making) process. Anti-corrosion additivesand preservatives can also be incorporated into the fiber network.

In addition or in the alternative, if the fibers are treated such thatcertain additives will adhere thereto, a fiber structure will resultthat incorporates the required additive/chemistry. That is, the requiredor desired property or properties is/are present in the lubricationsystem as long the fibers are contained in the lubrication system, e.g.,as a network or as a suspension/dispersion (e.g. a paste). For example,corrosion protection surfaces may be provided by the fiber structure incase an oil type will/can not function and a ‘paint’ type is notdesired.

High-Temperature Applications of the Present Lubricants

The above-mentioned known polymer-thickened grease technology disclosedin U.S. Pat. No. 5,874,391 is based on fully dissolving polypropylene(PP) in a base oil and uses the fact that a three-dimensional,phase-separated polymer structure is created if a relatively fastcooling rate is applied to the heated PP-oil mix. However, thistechnique has limited applications, because the grease is veryparticular to the polymer PP and quenching rate. Therefore, thestructure will lose its structure at operating temperatures above the PPmelting temperature, whilst significant softening starts well below thistemperature, such that the grease is suitable only for low to mediumtemperature applications.

On the other hand, one aspect of the present teachings distinguishesfrom known polymer-thickened grease technologies in that the structureis rendered substantially independent from the material and hence agrease-like structure can be obtained for a wide range of polymer fibermaterials. This avoids or eliminates the operating temperature limitthat exists for the above-mentioned known polymer-thickened greasetechnology.

Thus, in this application of the present teachings, a low to mediummelt-temperature polymer with lubricating properties in the fluid state(such as polypropylene (PP)) can be mixed with a fiber that is stable atrelatively high temperatures. At the high temperature, the lowermelt-temperature lubricating polymer will start to melt, therebyimproving the lubricating properties of the grease. In addition or inthe alternative, a fiber thickener may be utilized that has goodlubricating properties in its own right, such as PTFE, which exhibitshigh-temperature stability as well. Other very suitable candidatesinclude, but are not limited to, polysulfonates and other low meltingPTFEs.

It is preferred to integrate a PTFE or PES-type polymer into the fiberstructure, which will provide high temperature stability. Due to theinertness of PTFE, there will be little adhesion of these polymers tothe surfaces that need to be lubricated. Such adhesion issues can beovercome by mixing the high-temperature-stable fibers with otherpolymeric fibers that have higher adhesion properties, such as forexample PP. Thus, a mixture, e.g., of PP with PTFE and/or PES (and/oranother polymer) can improve the wetting/adhesion properties at hightemperatures.

For example, as was mentioned above, a polymer may be used that willmelt at a predetermined temperature, at which it begins to act as alubricant. If a mixture of polymer fibers having a range of meltingtemperatures is mixed into the structure of the grease, they willsequentially melt as the temperature increases. This would provide theadvantageous property that the fibrous polymers, which are incorporated(trapped) into the matrix of the grease, will not easily leak out untilthey start melting.

Fibers made from waxes as well as a mix of low molecular weight polymerscombined with high molecular weight oils also provide advantages forhigh temperature applications. In practice, the molecular weight thatcan be used remains limited to the limits of the melt blow (oralternative) production process utilized to form the fibers.

For example, a low molecular weight component of the polymer may act asa cross-link between strands of high molecular weight material. In thiscase, by adding, e.g., a ‘waxy’ polymer (i.e., low molecular weightvariant to the fiber chemistry) to the mixture, the mechanical stabilityof the grease will be improved by the formation of a physical connectionbetween loose strands of fiber.

The thickener preferably lubricates when it itself enters a tribologicalcontact, for example between a roller body and a raceway, such as existsin a bearing or another mechanical device. It is likely that thethickener will enter the contacts when the grease bleeds and it will bebeneficial that the thickener itself has lubricating properties.

If the above-mentioned properties can be influenced, a low meltingpolymer can be processed together with a high melting point polymer,whereby the first can contribute to the lubrication properties and thesecond can maintain the necessary stability of the lubricant, even athigh temperatures.

High Speed Applications of the Present Lubricants

The present teachings may be advantageously utilized in a variety ofdifferent applications with suitable modifications, including but notlimited to use in high speed and/or high temperature applications. Thebleeding property of the lubricant or grease can be tuned by adjustingthe fiber mix as was described above. In addition or in the alternative,the thermal and electric conductivity can be tuned and enhanced based onthe nature, density and mix of the fiber network. Thermal conductivityis very advantageous as it helps to reduce the temperature of high speedand high temperatures applications and lowers the risk of reachingtemperature limits that are defined by the materials used in theapplication, such as the lubricating oil(s), the polymer material(s),and the to-be-lubricated surface(s), such as a bearing cage.

In this aspect of the present teachings, fibers made from waxes, as wellas combinations of low molecular weight polymers combined with highmolecular weight oils, may be advantageously utilized. Waxes are goodnatural lubricants when pushed into the contacts.

The materials according to this aspect of the present teachings (fibrousgreases or porous networks) can be designed such that they will start tobleed oil at high speeds due to centrifugal forces. This feature of thepresent teachings is particularly advantageous in bearing applications,in which one or more cage bars are present, such as in cylindricalroller bearings (CRB), on which a lubricating grease resides. At lowspeeds, these greases preferably do not bleed oil, and only release oilat high speeds.

A preferred grease preferably has a high yield stress and well-balancedor uniform (even) bleeding characteristics. The high yield stress caneasily be obtained with the fiber-thickened greases according to thepresent teachings, because all the fibers themselves exhibit strongsolid-like rheological properties. This relates in part to thepossibility to fabricate a solid oil-like grease as described above.

At high speeds, centrifugal forces usually result in the oil beingexcessively depleted from the inner ring of a bearing. The wettingbehavior of the present greases enables them to capture a portion of theoil mist present inside the bearing during high speed applications. Iflocated in the inner ring, a parallel recirculation (absorption) of oilback to the inner ring will be created, thereby preventing excessive oildepletion as well as increasing the service life of the bearing.

On the other hand, the bleeding rate could be too low if theoil-retaining properties are too strong. In this case, no bleeding wouldoccur, which would result in no effective lubrication. This risk can bemitigated by increasing the bleeding rate by adjusting the oil affinityand mechanical stability of the fiber network.

Alternate Polymer Formulations for the Fibers

At least some of the above-noted polymers are based on using identicalpolymers with differing molecular weights. Two different polymers canpotentially also be used. Some examples include:

-   -   Charged and/or polar fibers, e.g. PAA-PM or PTFE, may be        combined with a (possibly low MW) oil dissolved polymer having        the opposite charge or polarity.    -   Amorphous fibers may be combined with a compatible        semi-crystalline connecting polymer (e.g., PEI fiber and PEEK).

Other possibilities include crystalline polymers, e.g., differentpolyesters, or other polymers with compatible surface energy, e.g.,polyamides having different polarity, e.g., different carbon chainlength per repeat unit, ranging up to PE which, when amide terminated,can conceptually be considered as PA infinite.

Further possibilities include the use of block-copolymers that arecompatible with the fibers, e.g., co-polyamides or co-polyesters withpolyamide or polyester fibers, respectively.

The rheological properties of hot-melt polyamides determine theglass-transition state in the polyamide. One of the very interestingconsequences of this is that the behavior of this material is relatednot only to a favorable hydrophilic/hydrophobic balance for lubricatingoils, but it also provides unique temperature-driven behavior andrheological behavior. The polymers can be chosen such that the glasstransition state is any temperature between 60-280° C.

Further, the flexibility of the material, e.g., the tensile strength,modulus, elongation etc., can all be tuned. In light of the abovediscussion concerning the potential mechanical weakness, the H-bondingcapacity of polyamide bonds makes them particularly advantageous. Inaddition, amides having functional side groups for cross-linking can beincorporated.

Improved Mechanical Stability of Greases According to the PresentTeachings

One important property of grease is its mechanical stability, by whichis meant the ability of the grease to maintain its rheologicalproperties after what is called working or over-rolling. Usually, theconsistency of a grease decreases after being mechanically ‘worked’ orstirred.

The mechanical stability of a complex fluid, such as grease, can beimproved if the structure is able to self-assemble after mechanicalshearing action into a structure that is similar to its structure beforethe disruptive action. For this re-assembly to occur, the basic buildingblocks of the structure (in this case nano- and micro-porous fibers)should self assemble into the original structure.

There are several options for achieving such self-assembly properties.

For example, either the entire fiber or a portion thereof may have apreferential affinity towards each other. This self-attracting affinitymay be greater than the affinity of the fiber to the lubricating oil. Inthis case, the fibers will self-assemble and form a percolating networkthat provides the sponge-like/grease structure. Bymanipulating/adjusting/controlling these affinities relative to eachother and to the oil, a wide range of structures can, in principle, beformed with varying amounts of mechanical stability and yield stress.

Thus, in this aspect of the present teachings, mechanical stability canbe increased by introducing areas into the fibers that have a designedaffinity towards each other and the lubricating fluid.

Heterogeneous fibers can be constructed, in principle, in many differentways. A few representative, non-limiting examples are provided:

A. The fibers can be randomly coated with a more polarmaterial/composition using a chemical or physical deposition method. Forexample, if a group of fibers is randomly sprayed with polarcoating/particles before being cut into smaller fiber lengths, a randomcollection of fibers can be obtained, many of which are at least partlypolar. In this manner, so-called Janus-type fibers (as described above)can be produced, in which one (or a part of one) side or end of thefiber has a different surface chemistry than the other part or end.

B. Heterogeneous fibers can be produced by mixing two polymers in thepolymer melt before the fibers are produced (for example, by meltblowing or another technique). Phase separation in the melt or coolingfluid leads to heterogeneous fibers. Examples known in the art of twonon-mixing polymers are legion and are not particularly limited in thepresent teachings. However, a few specific examples will be mentioned,such as, but not limited to a polar polymer like polyethylene oxide(PEO) and a non-polar polymer such as polystyrene (PS) or polypropylene(PP). The phase-separation and adherence of one phase to the other canbe increased by including so-called block co-polymers that are formed byconnecting one part of polymer A to another part of polymer B. In theabove example, this could be, e.g., PEO-PS or PEO-PP.

For the strength and stability of the grease and its fibers, theproperties of the polymer material can be selected to be optimal for theapplication conditions. Since the fibers will experience shear andcompressive forces of varying strength, the fibers should not be toobrittle, as breaking of the fibers will cause irreversible destructionof the fiber structure. The fiber material preferably has a relativelylow glass transition temperature (Tg), because polymers are more brittleat below their glass transition temperature (Tg) than above it.

An additional advantage is that polymers are more elastic and more‘sticky’ above their glass temperature. Elasticity is advantageous incertain application of the present teachings, because the fibers and theoverall fiber structure will be able to withstand shear forces betterthan highly rigid fibers that form a more brittle structure.

Relatively sticky polymers will provide a stronger bond at the locationswhere two fibers meet. Another benefit is that the friction forces oftwo fibers sliding over each other will be higher above the Tg and thisalso increases the strength of the network of entangled fibers.

As a representative example, atactic PP has a Tg of −20° C. Thus, PPfibers are preferably used at temperatures above −20° C., mostpreferably above −10° C. Similar considerations apply to other polymersand their glass transition temperature Tg.

In general, for low temperature applications, polymers having lowerglass transition temperatures should be selected, whereas polymershaving higher glass transition temperatures may be used for relativelyhigh temperature applications.

Seals Including Fibers According to the Present Teachings

In another aspect of the present teachings, fibers according to thepresent teachings (e.g., oleophilic fibers having a length generallybetween about 50 nm to 10 μm) may be incorporated into a seal, seal-lipor seal-lip dual layer, e.g., of a bearing or shaft seal, in order toreduce friction at the point(s) of contact or along a line of contact.Preferably, these fibers may be made of a low friction type of material(for example, PTFE, wax or similar materials), which does not migrate orbleed out of the resulting lubricant (after contacting the seal with thebase lubricating fluid). Alternatively, the oil-adsorbing property ofthe fibers according to the present teachings will ensure sufficientretention of oil within the sliding contact point or area, therebyreducing friction and wear.

In particular, wax-based or wax-like fibers are presently preferred forincorporation into seals in the dual material seal concept mentionedabove.

For example, a nano- or micro-fibrous network can be integrated into arubber/elastomeric seal in order to supply oil for lubricating the sealcontact. This aspect of the present teachings may be utilized to addressthe following problem. If a seal is not properly lubricated during itsoperation, an increase in friction will typically result with acorresponding increase in wear and operating temperature, which in turndecreases the service life of the seal.

Thus, in one exemplary embodiment, the fibers or a fibrous network maybe simply provided on a smooth surface of the seal (e.g., on the seallip), e.g., by rubbing the fibers onto the seal surface or by adheringthe fibers or a fibrous network onto the seal surface.

In another exemplary embodiment, one or more oil reservoirs, such as isshown in FIG. 1, is/are present or provided in the seal surface close tothe point(s) or line of contact of the moving parts. Such oil reservoirsare preferably capable of retaining and then releasing oil to thecontact point(s) or line, thereby reducing the likelihood of a poorlylubricated seal. In addition, friction will be reduced, therebyincreasing the seal life and sealing ability while also reducing therisk of leakages. Fibers according the present teachings are preferablydisposed (e.g., adhered) in such oil reservoirs in order to improve theoil retention/release properties of the oil reservoirs.

Preferably, such oil reservoir(s) is/are located at the ‘inside’ of thecontact. In addition or the alternative, the surface of the metal(steel) that contacts the seal lip may also have recesses adapted toretain oil. The oil reservoir(s) preferably have a largest internaldimension (e.g., an internal diameter) of about 10-200 μm.

In a preferred embodiment of this aspect of the present teachings, anoil-swollen seal lip or counter-face may be utilized. In suchembodiments, reduced friction can be achieved by incorporating orabsorbing oil into the seal lip materials. In this case, the oil willreside or be located more readily at the contact point(s) (line) of theseal (e.g., elastomer) and metal (e.g., steel shaft), thereby improvingthe supply of lubricant to the contact point(s) or line in need oflubrication. Reduced friction has many advantages, such as lower energyconsumption, lower operating temperatures, and longer seal and lubricantlife.

Oil swelling can be achieved by appropriately selecting or matching theaffinity of the oil (base lubricating fluid) with the elastomericmaterial forming the seal, e.g., by appropriately adjusting the amountof acrylo-nitrile content in NBR rubbers. By using a dual materialconcept, in which the tip is different from the bulk material, shapedeformation and other disadvantages relating to excessive swelling canbe reduced.

In another embodiment of this aspect of the present teachings, inaddition or in the alternative to swelling of the elastomer, the oilreservoirs are provided in the seal lip by creating a porous surfacearea that is capable of absorbing and/or retaining oil without resultingin significant swelling. The advantage of this aspect of the presentteachings is that the properties of the porous elastomer material can betuned (pore size, material stiffness, etc.) to achieve an optimumreservoir function but ideally also good wear resistance. Swollenelastomer materials are well-known to be more susceptible to degradationand wear.

Therefore, in this aspect of the present teachings, one or morelubricant reservoirs are provided or defined on and/or within a surfaceof the seal (e.g., the seal lip) that contacts a metal surface duringoperation, e.g., rotation of the seal lip relative to the metal surface(e.g., a shaft). The lubricant reservoir(s) preferably reduce friction,e.g., in a rotating sealing system, in order to achieve the reducedfriction advantages mentioned above. Fibers according to the presentteachings may be incorporated, adhered, disposed, etc. in the oilreservoir(s) to improve the oil retention properties.

The seals may be made from porous rubbers and polymers, e.g., nitrilerubber (NBR) and polyurethane (PU) materials, and can be producedaccording to any suitable technique known in the art. Other materialscan, in principle, be used as well. One example is to add salts, such asNaCl or CaCO₃, to the elastomer mixture prior to molding. After moldingthe seal, the salts are washed out of the seal lip using an aqueoussolution, thereby creating pores in the surface that are capable ofabsorbing, retaining and/or storing oil during operation of the seal.

The oil-swollen porous network may then be produced by adhering anoleophilic nano or micro-porous fiber network according to the presentteachings to the seal material, e.g., to the above-mentioned pores. Theadhesion is preferably strong enough to provide sufficient wearresistance. This can be achieved by using appropriate adhesion chemistryas is well known in the art. This porous network can also be adhered toa seal counterface (opposing) surface.

In another embodiment, a thicker ‘pad’-like structure comprising fibersaccording to the present teachings (e.g., a cloth, fabric, pad, mat,etc., as was discussed above) may be adhered to the seal or onto acounterface surface.

In another embodiment, a heterogeneous mixture of oil-swollen fibrousnetworks and commonly-used seal materials can be utilized to incorporatepockets of oil-swollen structures into the seal (or counterface)structure.

As the oil reservoir(s) is (are) only needed near the seal lip, thesurface layer (liner) may be porous and may be combined with a standardseal material (such as NBR). If the two materials are the same (e.g.,both NBR or PU), they can be more readily bonded together during thecross-linking step. This prevents adhesion problems in the bonding layerthat might arise when friction forces apply stress to this layer.

FIG. 2 shows a schematic example of a representative dual material seallip comprising a porous liner layer 1 that is capable ofabsorbing/releasing oil and a bulk seal material 2 that supports theporous liner layer 1. The bulk seal material 2 is attached to a steelsupport 3 for further support. The porous liner layer 1 is preferablyformed according to the above-mentioned embodiments, i.e. fibers arepreferably disposed in oil reservoirs defined in the layer. The fibersmay be embedded or incorporated into the material of the porous linerlayer 1, e.g., by mixing the fibers with a suitable elastomeric materialprior to molding. However, the fibers may also be adhered to the porousliner layer 1 after the porous liner layer 1 has been formed or thefibers may even by simply deposited onto the surface of the porous linerlayer 1, e.g. by rubbing or spraying or otherwise coating.

Bearing Cages Including Fibers According to the Present Teachings

In another embodiment of the present teachings, fibers according to thepresent teachings may be incorporated into a cage of a rolling elementbearing. The cage is a source of friction for the rolling elementsdisposed in the bearing and thus a reduction in friction would beadvantageous in such bearing applications.

In some known bearings, the cage bars or struts (the portions thatseparate or space the rolling elements) contain a grease reservoir (ifthe bearing is grease lubricated) that supplies the bearing with oil.Therefore, in this aspect of the present teachings, a grease-like porousfiber network or a structurally more rigid network (with longerinterconnected fibers) is preferably located in or on the cage, e.g., inone or more grease reservoirs. Preferably, this porous network islocated on a surface of the cage bar(s) adjacent to the rollingelement(s) (e.g., roller bodies, such as ball bearings orcylindrical/tapered rollers) so as to be close enough to the rollingelements that need to be lubricated.

The fibrous network can be physically or chemically attached/adhered tothe surface of the cage (e.g., the bars or struts) using adhesionchemistry technology known in the art. In the alternative, fibersaccording to the present teachings can be rubbed or otherwise depositedonto the surface of the cage or struts prior to assembling the bearing.The cage can be made from metals (sheet metal, steel, brass, forexample) or from hard polymers. In case the cage is made of a polymermaterial, it is also possible to incorporate or embed the fibers intothe surface of the cage when manufacturing (e.g., injection molding) thecage.

Friction can be reduced by disposing the fibrous network on the side ofthe cage bar(s) that is (are) in contact with the rolling elements (i.e.against which the cage bar(s) slide(s)). The temperature stability ofthe fibrous network can be tuned/adapted/adjusted by appropriatelyselecting the polymeric materials forming the fibers, as was describedabove.

One of the main reasons for reduced service life when grease is usedwith a steel cage is the fact that the cage scrapes on (frictionallycontacts) the roller elements (bodies) during operation. Of course, apolymer material cage will also frictionally contact the rollingelements during operation, but the polymer cage redistributes the thinlayer of oil that is adhered to the rolling elements rather than scrapesit off.

Therefore, in another aspect of the present teachings, a soft,fabric-like material made of the present fibers (as was described inmore detail above) can be attached the cage (e.g., the cage bars). Inthis case, the fabric material (fibrous network) will gently wipe theadjacent rolling element(s) during the operation, thereby redistributingthe lubricant layers and causing locally thin layers to be “repaired”and/or replenished. This property will enhance the grease life andbearing life.

For example, one or more lubricant (oil) reservoirs may be provided ordefined in the bearing cage. A PA fiber mat may be disposed in thelubricant reservoir(s) or cavities and then overmolded. The PA fiberpreferably acts like a sponge for retaining and releasing thelubricating fluid or oil.

This aspect of the present teachings preferably utilizes the phenomenonof super-cooling in an advantageous manner. For example, the meltingpoint of the polymer is preferably higher than its crystallisationtemperature. In this case, it may be possible to overmold the fiber matwithout melting all of the fiber mat. The highest melting points occurin fibers.

The molding process parameters may be optimized, e.g., to provide goodcompatibility with seal materials and/or cages. This property could beused to increase the bearing speed rating by providing a “sticky”thickener on the “splash surface” Improved lubrication of land-ridingcage surfaces also may be provided.

An oleophilic CoPA (PA co-polymer) optionally may be added to improvethe PA cage surface affinity with oleophilic thickeners, as will befurther described below.

Other Bearing Types Utilizing Fibers According to the Present Teachings

Using the same principle, a fiber structure may be disposed onplane-bearing liners or on washers to improve tribologicalfunctionality. By having fibers anchored in the polymer matrix, a highcompression strength matrix can be combined with a low friction surface.

Water Absorbtion Functionality

Melt-spinnable fibers can have very different chemical properties. Forexample, their behavior can also be tuned to be very hydrophilic and inthis case, the fibers will exhibit a very high affinity to water. Suchhygroscopic fibers are capable of advantageously eliminating (absorbing)any free water in the lubrication system as well as any dissolved water.If placed in or on a seal, they can act as an active water removaldevice for industrial lubricants.

One particularly advantageous example of such a system is a sealedbearing wherein the seal is able to adsorb water, which would otherwisebe very harmful to the bearing system. Water can result in corrosionand/or hydrolysis of the lubricant, for example, leading to earlyfailures.

Thus, in certain aspects of the present teachings, hydrophilic and/orhygroscopic fibers may be disposed on the surface of a seal in additionor in the alternative to the above-described oleophilic fibers.

Fibers Applied to a Bearing Surface Utilizing a Melt-Spinning Process

A melt-spinning process can be used to directly apply fibers accordingto the present teachings onto the surface of a metallic conductor (e.g.,a gear, bearing raceway, axial screws, etc), thereby leading to in situdeposition and a very cost-effective way of using the fibers as anin-service lubricant. The fibers may be sprayed directly onto thebearing/seal or cage surfaces in the production line and then allowed tocool. This manufacturing step could be performed in various ways, e.g.,by controlling both the speed of spraying and rotating the targetsurfaces. This process will result in a fiber coating on the bearingsurface that will adsorb oil. In one embodiment, the fibers are producedusing melt-blowing techniques that directly apply the fibers onto thetarget object. In an alternative embodiment, electro-spinning processescan be utilized for very accurate fiber production and depositioncontrol onto the metallic objects.

In one embodiment thereof, the fibers may function as a preservative(corrosion-preventing substance) for the bearing. The fibers (e.g.,applied according the above-described spray-on method) may be used toform, together with an oil, a preservative, i.e. a grease-like layer toprevent corrosion of the metallic bearing or a similar object. Thissprayed-on fiber layer can also facilitate beneficial running-in, whenappropriate additives are present.

The same applies for conductive seals and cages according to thepreceding embodiments.

If the seal or cage polymers are not conductive, another option is touse the super cooling effect so that overmolding is possible.

Application of such a fiber sponge (network) could also be utilized intransport systems (conveyor belt, for example) to improve productionprocesses that suffer in many cases from poor lubrication and thusresult in wear contamination of the objects that are being transported.It is also possible to make use of the oleophilic properties of thefiber material to lubricate and hold the oil, which would stop orprevent unwanted excessive oil leakage or contamination onto theproducts being transported.

Tunable Co-Polymer Fibers

As was mentioned above, an oleophilic CoPA (PA co-polymer) may beincorporated in order to improve the PA cage surface affinity witholeophilic thickeners. For example, block copolymers may be used as thethickener fiber material, which will improve structural integrity.

Polyamide hydrocarbon technology is particularly advantageous, becauseit allows one to make more hydrophobic polyamide-based resins that havedifferent compatibility with oil and water than polyamide itself. Thistechnology may be particular advantageous if ester oils or other polaroils are used.

In addition or in the alternative, in order to improve grease retention,amide tackifiers may be used to connect amorphous fibers as additives inPA cages.

A variety of modifications may be utilized in order to tune or adapt theoleophilicity and oil compatibility. For example, polymer molecules maybe synthesized based on two types of chemical groups, e.g., wherein oneis more oleophilic (or non-polar) and the other is more hydrophilic(polar). This can be implemented in a number of ways, such as, e.g.,changing the chain length of the hydrocarbon in order to alter thehydrophobic properties of the polymer. If fibers are made from thesepolymers, the oleophilic nature may be tuned in accordance with thelength of the hydrocarbon (HC) chains. Thus, this aspect of the presentteachings not only enables the oil compatibility of the cages to betuned, but also the fibers.

Thus, whereas polyamides used for the cage material are a largelycrystalline material, polyamides incorporating fatty acids will belargely amorphous in structure. In this case, tackifiers may be used toconnect amorphous fibers.

The rheological properties of hot-melt polyamides may also be used inthis aspect of the present teachings.

The grease proposed in this aspect of the present teachings, e.g., usingpolyamides fibers, is preferably able to:

-   -   create a large degree of freedom in the        hydrophilicitiy/hydrophobicitiy balance in the thickener,    -   tune the rheological properties of the thickener to match        desired grease properties,    -   tune temperature-dependent behavior to match grease requirements        for applications, or create temperature-triggers, and    -   incorporate functional side groups for cross-linking, in order        to immobilize the network structure in the thickener.

In the adhesion properties of the fibers, their ‘tackiness’ becomes animportant property. Therefore, methods for tuning that property aresignificant in this aspect of the present teachings. One importantcharacteristic of lubricating grease, as compared to oil, is that it‘stays in place’. Thus, the grease needs to be “thick” and must “stick”in order to be effective. The ability to stay in place is not just amatter of grease viscosity but also a matter of the ability to stick(adhere) to other surfaces. This phenomena is called tackiness and canbe explained as a substance's ability to be cohesive (stick to itself)and adhesive (stick to other surfaces).

The polymers forming the thickener of the grease can be used as“tackifiers”. Traditional tackifiers are polymers of high molecularweight, typically in the range from 400,000 to 4,000,000. As one uniqueproperty of the fiber-thickened grease according to this aspect of thepresent teachings, using polymers molecules as the thickener materialand coating the polymers to provide adhesion makes it possible to tuneboth cohesion and adhesion while controlling bleeding (oil loss).

Self-Generating and Self-Assembling Grease

Another aspect of the present teachings concerns embodiments, whichenable oil to be pumped or moved within the lubrication system, butwherein the moving parts are lubricated with greases, such as in agearbox.

In one embodiment of this aspect of the present teachings, polymer fiberthickeners and oils may be sprayed inside bearings separately in orderto form a self-generating grease inside the bearing. For this purpose,polymer fibers may be processed, e.g., into granules or particles. Oilsmay then be subsequently sprayed into the bearing separately, e.g., as afine oil mist. The oil and polymer fiber particles will then (re)combinein situ to form a grease.

In another embodiment, the fibers may be produced, e.g., by melt-blowingor electro-spinning, and then deposited onto the surface of gears,gearboxes, bearings, etc. The oil is added separately or just beforeapplication to the mechanical system.

One advantage of this embodiment is that pumping of oil is easier (lessenergy intensive) than pumping of thick grease, because oil is lessviscous. Thus, energy consumption may be reduced without sacrificinglubricating performance.

Another advantages of this embodiment is that the distribution of greaseinside the bearing, e.g., on the cage, or in the rolling contact, can befully controlled.

Another advantage is the complete freedom and variability of greaseformulation depending on re-lubrication needs and operating conditions.

Another advantage is that the bearing may be lubricated with oil toensure replenishment of the rolling contact, wherein excess oil isadsorbed in the shape and form of grease.

Advanced Lubrication Systems Using Self-Generating and Self-AssemblingGrease

Known automatic lubrication systems are currently used for intermittentlubrication and re-lubrication of bearing applications. In comparisonwith oil lubrication, grease lubrication is limited by high viscositygrease flow and the risk of blocked lines or conduits.

In addition, grease lubrication properties and grease stability may beaffected when pumping greases through lines or pipes that are typicallynarrow, thereby potentially reducing lubrication performance.

Moreover, pumping of grease requires high pressures and large pumps,owing to the ‘thick’ or viscous nature of grease. Of course, largerpumps operating at higher pressures require more energy as well as morespace.

Thus, this aspect of the present teachings overcomes the disadvantagesof known grease pumping systems, because oil may be pumped to theto-be-lubricated surface, instead of grease.

Further, in this aspect of the present teachings, polymer fibers forgrease thickening may be combined with base oil in a new type of pumpingsystem. In this system, base oil is pumped through a pumping linetowards the intended point for re-lubrication, where it is combined witha separate addition of fibers according to the present teachings, e.g.,polymer fibers. These fibers may be sprayed, pumped, or be alreadypresent on the contact surface. Polymer fibers may consist of, e.g.,solid powder particles.

Consequently, the base oil and polymer thickener fibers may be pumpedtowards the re-lubrication point without any limitation on pumping,pumping speed or line blockage. Additionally, through direct mixing,there is no effect on grease stability, aging or lubricationperformance.

In addition, the grease can be formulated so that a re-lubricationformulation is possible in-line. That is, when grease for re-lubricationis formulated “in-line”, its composition and properties may be varied tomatch varying application (usage) conditions. As a non-limiting example,re-lubrication of main shaft bearings in wind turbines is typicallyperformed under varying conditions, including the ambient conditions(cold weather, summer weather), the running-in phase, stormconditions/vibrating conditions, etc. For cold weather, grease having alower consistency or viscosity typically is more advantageous thangreases having a high consistency or viscosity. During a hot summer, theopposite is true. By varying the grease formulation depending on summeror winter conditions, lubrication may be optimized. Variation of greaseformulations may be integrated into the re-lubrication control system.It is possible to mix complex fluids such as greases from a base.

Bearing Specific Applications

In U.S. Pat. No. 7,275,319, the effect of making dimples on rollingbearing surfaces was described. Dimples improve the build-up of alubricant film in the case of starved (i.e. insufficient grease)lubrication. The dimples are assumed to carry lubricant to the contactsand release the lubricant in the inlet of the contact, thereby makingthe contacts less starved and resulting in an increase of thelubricating film. The dimples are preferably refilled prior to startingthe next contact cycle. The '319 patent discloses the option of coatingthe surfaces with an oleophilic film that would facilitate thereplenishment of the dimples.

According to the present teachings, a corresponding coating can beprovided by the fiber thickened grease in which oleophilic fibersaccording to the present teachings are utilized. The fibers may besheared off on the lands between the dimples where the “severity” of thecontact is very strong. In the dimples themselves, the contacts stressesare lower and no metal-to-metal contact will occur. This means that suchmaterial will not be easily removed from this spot and therefore, suchmaterial is an optimal lubricant for these bearing applications.

The same idea can also be used for bearing surfaces with a clear lay,such as hard-turned or cross-honed surfaces. The contact intensity willbe high on the top of the roughness grooves and, in the case of mixedlubrication, metal-to-metal contact will occur here. The oleophilicgrease material will stay in the lower part of the surface topographybut will promote replenishment of the top of the grooves by driving alubricant flow.

Friction Reduction at Metal Contacts

In another embodiment of the present teachings, a nano-fibrousfabric-like material made with fibers according to the present teachingsmay be used as an anti-fretting solution. The porous and thin layer willretain oil and the added local lubrication will reduce fretting.

Electrostatic fiber spinning may be utilized to deposit the fibers onthe bearings, e.g., on the outer ring of the bearing, to preventfretting.

By electro-spraying the various polymers, including wax types, the fiberstructured material (directly spun onto the surface) opens thepossibility of preserving (preventing corrosion of) large bearings,avoiding oil leakage and decreasing the corrosion risk caused by aprotective film that is too thin.

In addition, the present teachings may be advantageously combined withthe above-noted teachings from '319 patent concerning dimples, and thusthe contents of the '319 patent, in particular the description of thedimples, are fully incorporated herein by reference.

In addition, the creation of a dampening surface between metalliccomponents will reduce vibration and noise levels. Wear will be reducedby smoothing the surface (by replenishment) and this will reduce theamount of metallic debris in the contact zone and therefore furtherreduce wear and noise. Shafts, bearing rings and other components aresuitable for this protection mechanism.

In another aspect of the present teachings, a type of wick may bedisposed so as to make sliding contact between the inner and outer ring,e.g., like a seal made of a fibrous network or fabric. In thisembodiment, the wick can transport oil from the inner ring to the outerring or the oil from regions of high oil content to regions of low oilcontent. This cloth can also be adhered to the seal itself.

Fibers Deposited on a Surface

In any of the above-mentioned embodiments, in which fibers are depositedonto (e.g., rubbed onto, adhered to, embedded or incorporated in, etc.)a surface in need of lubrication in order to, e.g., form aself-generating thickened lubricant upon contact with a lubricatingfluid or other oil, or to provide lubricating functionality themselves(e.g., as ‘dry’ lubricants), the thickness of the fibers may be betweenone monolayer of fibers (or fabric material) to tens of layers up tohundreds of layers. Particularly preferred ranges are between 1-50layers, more preferably 2-20 layers.

EXPERIMENTAL EXAMPLES

The following representative examples demonstrate the ability to formfiber-thickened oils with grease-like properties according to thepresent teachings. In all examples, cone penetration was determined inaccordance with the standard ASTM D217-10 (worked penetration after 60strokes at 25° C.). Usual consistencies of NLGI classes 0-3 wereobtained in all examples.

In the following Examples 1-6, the fibers were initially provided in theform of a cloth on a roll, which was subsequently broken by both ahomogenizer and the strain applied by a 3-roll mill The 3-roll mill is adevice that is sometimes used in the art to add additives to greasecompositions or to perform other mechanical ‘working’ and homogenizationon the grease.

Example 1

Polypropylene (PP) fibers having an average fiber diameter of about 400nm were mixed with polyalphaolefin (PAO) having a base oil viscosity of48 cSt at 40° C. The fiber density was 5.6%. The cone penetration was37.3 mm and the NLGI grade or consistency was 0.

Example 2

Polypropylene (PP) fibers having an average fiber diameter of about 400nm were mixed with polyalphaolefin (PAO) having a base oil viscosity of48 cSt at 40° C. The fiber density was 5.9%. The cone penetration was365 mm and the NLGI grade or consistency was 0.

Example 3

Polypropylene (PP) fibers having an average fiber diameter of about 400nm were mixed with polyalphaolefin (PAO) having a base oil viscosity of48 cSt at 40° C. The fiber density was 6.6%. The cone penetration was347 mm and the NLGI grade or consistency was 0/1.

Example 4

Polypropylene (PP) fibers having an average fiber diameter of about 400nm were mixed with polyalphaolefin (PAO) having a base oil viscosity of48 cSt at 40° C. The fiber density was 7.3%. The cone penetration was324 mm and the NLGI grade or consistency was 1.

Example 5

Polypropylene (PP) fibers having an average fiber diameter of about 400nm were mixed with polyalphaolefin (PAO) having a base oil viscosity of48 cSt at 40° C. The fiber density was 7.9%. The cone penetration was313 mm and the NLGI grade or consistency was 1.

Example 6

Polypropylene (PP) fibers having an average fiber diameter of about 400nm were mixed with polyalphaolefin (PAO) having a base oil viscosity of48 cSt at 40° C. The fiber density was 10%. The cone penetration was 230mm and the NLGI grade or consistency was 3.

FIG. 3 graphically shows the change in grease consistency withincreasing fiber density.

Additional embodiments of the present teachings disclosed hereininclude, but are not limited to:

1. A grease comprising an oil and/or lubricating fluid and thickeningfibers having a length in the micron range and a diameter or width inthe micron or nanometer range, the fibers being oleophilic.

2. A grease according to embodiment 1, wherein the fibers comprise atleast two portions having different physical and/or chemical properties.

3. A grease according to embodiment 2, wherein at least one of theportions has a higher affinity to a like portion than to the oil and/orlubricating fluid, thereby imparting a self-assembly property to thethickening fibers.

4. A grease according to any preceding embodiment, wherein the fibershave a length of 100-500 microns.

5. A grease according to embodiment 4, further comprising oleophilicthickening fibers having a length of 1-100 microns.

6. A grease according to any one of embodiments 1-3, wherein the fibershave a length of 1-100 microns.

7. A grease according to any preceding embodiment, wherein the fibershave a length that is at least about 5-10 times the diameter thereof.

8. A grease according to any preceding embodiment, wherein thethickening fibers are a mixture of organic fibers, e.g., polypropylene,and inorganic, e.g., ceramics, e.g., aluminum oxide and/or silicondioxide.

9. A grease according to any preceding embodiment, wherein the fibersalso have oleophobic and/or hydrophilic properties.

10. A grease according to any preceding embodiment, further comprisingnon-oleophilic fibers having oleophobic and/or hydrophilic and/orhygroscopic properties.

11. A grease according to any preceding embodiment, wherein the fibersare biodegradable.

12. A grease according to any preceding embodiment, wherein thethickening fibers comprise cellulose and/or gum.

13. A grease according to any preceding embodiment, wherein thethickening fibers are coated, e.g., randomly coated, with a compositionthat is more polar than the thickening fiber.

14. A grease according to any preceding embodiment, wherein thethickening fibers comprise Janus fibers.

15. A grease according to any preceding embodiment, wherein thethickening fibers are comprised of a mixture of at least one polarpolymer, e.g., polyethylene oxide (PEO), and at least one non-polarpolymer, such as polystyrene (PS) or polypropylene (PP).

16. A grease according to embodiment 15, wherein the fiber is a blockco-polymer.

17. A grease according to any preceding embodiment, wherein the fibershave a strong affinity for steel and/or polymer surfaces.

18. A grease according to any preceding embodiment, wherein the fibersform a sponge-like network that absorbs or retains the lubricating fluidor oil.

19. A grease according to embodiment 18, wherein the sponge-like networkhas the property that it shrinks or contracts as the temperatureincreases, thereby squeezing out lubricating fluid or oil.

20. A grease according to any preceding embodiment, wherein the greasecomprises at least two types of thickening fibers, each having adifferent melting temperature.

21. A grease according to embodiment 20, wherein at least the thickeningfiber having the lowest melting temperature acts as a lubricant when thegrease is brought to a temperature above the melting temperature of saidthickening fiber.

22. A grease according to any preceding embodiment, wherein thethickening fibers are formed from a wax and/or further comprising wax.

23. A grease according to any preceding embodiment, further comprising alow molecular weight polymer, e.g., a wax, that cross-links thickeningfibers having a higher molecular weight.

24. A grease according to embodiment 22 or 23, wherein the wax is anatural wax or a hydrocarbon wax.

25. A grease according to embodiment 24, wherein the wax is bees wax orparaffin wax.

26. A grease according to any preceding embodiment, wherein thethickening fiber is a tackifier or further comprising a tackifier.

27. A grease according to any preceding embodiment, wherein thethickening fibers and the lubricating fluid or oil are selected suchthat the thickening fibers are capable of self-generating a fibroussponge-like network when the thickening fibers contact the lubricatingfluid or oil.

28. A fiber according to any preceding embodiment (i.e. without the oilor lubricating fluid), preferably constituting between about 0.1 and 100wt % of a final material, more preferably about 50-100 wt %.

29. A bearing surface coated with a fiber according to embodiment 28 orhaving a fiber according to embodiment 28 embedded or incorporated intothe bearing surface, the bearing surface preferably comprising steel.

30. A seal coated with a fiber according to embodiment 28 or having afiber according to embodiment 28 embedded or incorporated into thesurface of the seal, the seal optionally comprising an elastomericmaterial, e.g., NBR or polyurethane and/or wax fibers disposed in theseal.

31. A bearing cage coated with a fiber according to embodiment 28 orhaving a fiber according to embodiment 28 embedded or incorporated intothe surface of the cage, the cage preferably comprising steel orpolyamide.

32. A bearing surface or seal or bearing cage according to embodiments29-31, respectively, having a plurality of oil reservoirs defined in thebearing surface or seal surface or cage surface, respectively, thefibers and oil reservoirs being located at least a primary point ofcontact between two parts moving relative to each other duringoperation.

33. A bearing surface or seal or bearing cage according to embodiments29-31, respectively, having a porous surface structure and/or a surfacestructure that has been chemically treated to cause lubricating fluid oroil to be released from the grease under prescribed operatingconditions.

34. A grease, fiber, seal or bearing cage according to any precedingembodiment, wherein the oleophilic thickening fibers have a diameterbetween about 50 nm and 10 microns, and more preferably between about100 nm and 1 micron.

35. A grease, fiber, seal or bearing cage according to any precedingembodiment, wherein the oil and/or lubricating fluid comprises one ormore of mineral oil obtained from crude oil, group I, II and IIIlubricants, group IV lubricants (polyalphaolefins “PAO”) and group Vlubricants (all others).

36. A grease, fiber, seal or bearing cage according to any precedingembodiment, wherein the oil and/or lubricating fluid comprises one ormore of mineral oil, synthetic ester, and plant-based oil and theirderivatives, such as oils derived from rapeseed, canola, sunflower,canola and palm.

37. A grease, fiber, seal or bearing cage according to any precedingembodiment, wherein the oil and/or lubricating fluid comprises one ormore of animal-based oils, their derivatives and synthetic lubricantssuch as polyglycols (PG), polyalkylene glycol (PAG), white oils,silicone oils, very-high viscosity index oils (VHVI), water, glyceroland waxes.

38. A grease, fiber, seal or bearing cage according to any precedingembodiment, wherein the oil and/or lubricating fluid has a viscositythat is between about 1-1000 cSt at 40° C.

39. A grease, fiber, seal or bearing cage according to any precedingembodiment, wherein the fibers comprise a polymeric material that hasbeen spun into fibers.

40. A grease, fiber, seal or bearing cage according to any precedingembodiment, wherein the fibers comprise one or more of polyamide (PA),nylon 6,6, polyamide-6,6 (PA-6,6), polyamide-4,6 (PA-4,6), polyurethanes(PU), polybenzimidazole (PBI), polycarbonate (PC), polyacrylinitrile(PAN), acrylonitrile rubber (NBR), polyvinylalcohol (PVA), polylacticacid (PLA), polyethylene-co-vinyl-acetate (PEVA), PEVA, polymethacryate(PMMA), tetrahydroperfluorooctylacrylate (TAN), polyethylene oxide(PEO), collagen-PEO, polyaniline (PANI), polystyrene (PS), silk-likepolymer with fibronectin functionality, polyninylcarbazole, polyethylenererephtalate (PET), polyacrylic acid (PAA), polypyrene methanol (PM),polyvinylphenol (PVP), polyvinylchloride (PVC), cellulose acetate (CA),polyacrylamide (PAAm), PLGA, collagen, polycaprolactone (PCL),poly(2-hydroxyethyl methacrylate) (HEMA), poly(vinylidene fluoride)(PVDF), polyether imide (PEI), polyethylene glycol (PEG),poly(ferrocenyldimethylsilane) (PFDMS), poly(ethylene-co-vinyl alcohol),polyvinyl pyrrolidone (PVP), polymetha-phenylene isophthalamide,polypropylene (PP), polyethylene naphthalate (PEN), Teflon®,polytetrafluorethene (PTFE), waxes, waxy polymers, polyolefins,polyesters, and polysulfones.

41. A grease, fiber, seal or bearing cage according to any precedingembodiment, wherein the fiber comprises one or more polymers derivedfrom a natural or biodegradable source, such as, e.g., polysaccharides,such as cellulose, starch, chitin, chitosan, proteins, (poly)peptidesand gelatin.

The preferred embodiments and exemplary examples were described above incombinations of features and steps that may not be necessary to practicethe invention in the broadest sense, and such detailed combinations havebeen described merely for the purpose of particularly describingrepresentative examples of the invention. Furthermore, various featuresof the above-described representative examples, as well as the variousindependent and dependent claims, may be combined in ways that are notspecifically and explicitly enumerated in order to provide additionaluseful embodiments of the present teachings.

All features, oils, base lubricating fluids, materials, polymers,fibers, additives, etc. disclosed in the description and/or the claimsare intended to be disclosed separately and independently from eachother for the purpose of original written disclosure, as well as for thepurpose of restricting the claimed subject matter, independent of thecompositions of the features in the embodiments and/or the claims. Inaddition, all value ranges or indications of groups of entities areintended to disclose every possible intermediate value or intermediateentity for the purpose of original written disclosure, as well as forthe purpose of restricting the claimed subject matter.

1. A dry lubricant comprising at least 50 wt % of fibers having adiameter between 50 nm and 10 microns and a length that is at least 5times the diameter.
 2. The dry lubricant according to claim 1, whereinthe fibers have a diameter between 100 nm and 1 micron.
 3. The drylubricant according to claim 1, wherein the fibers are comprised of apolymeric material that has been spun into fibers.
 4. The dry lubricantaccording to claim 1, wherein the fibers comprise one or more at leastone of polyamide (PA), nylon 6,6, polyamide-6,6 (PA-6,6), polyamide-4,6(PA-4,6), polyurethanes (PU), polybenzimidazole (PBI), polycarbonate(PC), polyacrylinitrile (PAN), acrylonitrile rubber (NBR),polyvinylalcohol (PVA), polylactic acid (PLA),polyethylene-co-vinyl-acetate (PEVA), PEVA, polymethacryate (PMMA),tetrahydroperfluorooctylacrylate (TAN), polyethylene oxide (PEO),collagen-PEO, polyaniline (PANI), polystyrene (PS), silk-like polymerwith fibronectin functionality, polyninylcarbazole, polyethylenererephtalate (PET), polyacrylic acid (PAA), polypyrene methanol (PM),polyvinylphenol (PVP), polyvinylchloride (PVC), cellulose acetate (CA),polyacrylamide (PAAm), PLGA, collagen, polycaprolactone (PCL),poly(2-hydroxyethyl methacrylate) (HEMA), poly(vinylidene fluoride)(PVDF), polyether imide (PEI), polyethylene glycol (PEG),poly(ferrocenyldimethylsilane) (PFDMS), poly(ethylene-co-vinyl alcohol),polyvinyl pyrrolidone (PVP), polymetha-phenylene isophthalamide,polypropylene (PP), polyethylene naphthalate (PEN), Teflon®,polytetrafluorethene (PTFE), waxes, waxy polymers, polyolefins,polyesters, polysulfones and polyethersulfones (PES).
 5. The drylubricant according to claim 1, wherein the fibers comprise at least onepolymers derived from a natural or biodegradable source, such ascellulose, starch, chitin, chitosan, proteins, (poly)peptides andgelatin.
 6. The dry lubricant according to claim 1, wherein the fibersare a mixture of organic fibers.
 7. The dry lubricant according to claim1, wherein the dry lubricant comprises at least two types of the fibers,each having a different melting temperature.
 8. The dry lubricantaccording to claim 7, wherein at least the fiber having the lowestmelting temperature acts as a lubricant when the dry lubricant isbrought to a temperature above the melting temperature of said fiber. 9.The dry lubricant according to any claim 7, wherein at least one of thetwo types of fibers is at least substantially comprised of a wax. 10.The dry lubricant according to claim 9, wherein the wax is a natural waxor a hydrocarbon wax.
 11. The dry lubricant according to claim 10,wherein the wax is bees wax or paraffin wax.
 12. The dry lubricantaccording to claim 1, wherein at least one of the two types of fibers isat least substantially comprised of PTFE and/or PES.
 13. The drylubricant according to claim 1, wherein the fibers are loose strandsadhered or cross-linked by a compound having a lower molecular weightthan the fibers.
 14. The dry lubricant according to claim 13, whereinthe compound having the lower molecular weight is a wax.
 15. The drylubricant according to claim 1, wherein the fibers are oleophilic. 16.The dry lubricant according to claim 15, further comprising hydrophilicfibers having a diameter between 50 nm and 10 microns and a length thatis at least 5 times the diameter.
 17. The dry lubricant according toclaim 16, wherein hydrophilic fibers are hygroscopic.
 18. The drylubricant according to claim 15, wherein the oleophilic fibers alsoexhibit at least one of the oleophobic and/or and hydrophilicproperties.
 19. The dry lubricant according to claim 1, wherein thefibers are biodegradable.
 20. The dry lubricant according to claim 1,wherein the fibers comprise at least one of cellulose and gum.
 21. Thedry lubricant according to claim 1, wherein the fibers are coated, e.g.,randomly coated, with a composition that is more polar than the fibers.22. The dry lubricant according to claim 1, wherein the fibers compriseat least two portions having at least one of different physical andchemical properties.
 23. The dry lubricant according to claim 1, whereinthe fibers are comprised of a mixture of at least one polar polymer, andat least one non-polar polymer.
 24. The dry lubricant according to claim1, wherein the fibers have a strong affinity for at least one of steeland polymer surfaces.
 25. The dry lubricant according to claim 1,wherein the dry lubricant comprises at least 70 wt % of the fibershaving a diameter between 50 nm and 10 microns and a length that is atleast 5 times the diameter.
 26. The dry lubricant according to claim 1,wherein the dry lubricant comprises at least 95 wt % of said fibershaving a diameter between 50 nm and 10 microns and a length that is atleast 5 times the diameter.
 27. (canceled)
 28. The dry lubricantaccording to claim 1, wherein the dry lubricant comprises at least 80 wt% of the fibers having a diameter between 50 nm and 10 microns and alength that is at least 5 times the diameter.
 29. The dry lubricantaccording to claim 1, wherein the dry lubricant comprises at least 90 wt% of the fibers having a diameter between 50 nm and 10 microns and alength that is at least 5 times the diameter.